This invention relates generally to the control of heat pump and air conditioning systems and, more particularly, to speed control of a variable speed compressor in a multiple zone air conditioning system. A basic air conditioning system of the type usually found in residences comprises a heating/cooling unit which is controlled by a single thermostat to provide a constant volume of heating or cooling air during periods when the room temperature differs from the thermostat set point by a predetermined amount. Such a system has been found unsuitable for larger buildings where there are multiple use areas with different mode requirements. To accommodate these requirements, a multiple zone system was introduced and is now common in the industry. Such a multiple zone system has multiple thermostats, with each thermostat controlling the flow of cooling/heating air to its particular zone.
One type of multiple zone system is that known as the VVT (variable volume and temperature) system which is commercially available from Parker Electronics Inc. This system, which is described in U.S. Pat. No. 4,530,395 issued to Jeffrey L. Parker et al. on July 23, 1985 and is incorporated herein by reference, includes a microcomputer based thermostat and damper assemblies to modulate the air flows and temperatures to maintain the desired amounts of air flow to the respective zones. Such a system is designed to operate with a single speed compressor whose capacity is greater than any anticipated load such that it is usually operating in an oversized condition. Initially, the individual zone dampers are all in the fully opened position, but as the zone temperatures get closer to the respective thermostat set points, their respective dampers begin to modulate to the closed positions. Accordingly, in those zones where the set point temperatures have been met, the dampers will be closed, whereas in the other zones, the dampers will either be fully opened or will be in the process of modulating toward the closed position. In order that proper air flow is maintained, there will always be one damper which remains fully opened: but the remaining dampers will eventually close and finally the system will shut off when all of the thermostat set points have been met. It will thus be seen that the dampers tend to operate primarily in the fully opened or fully closed positions, with the period of modulation between those extreme positions being limited to relatively small periods of time.
It is therefore an object of the present invention to provide an improved air conditioning temperature control system.
Another object of the present invention is the provision in an air conditioning system for more closely matching the capacity of the system with the existing load thereon.
Still another object of the present invention is the provision in a multizone air conditioning system for maintaining control of the air flow to the zones for a greater percentage of time.
Yet another object of the present invention is the provision for an air conditioning control system which is very functional in use and economical to manufacture and operate.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.